[RFC PATCH] tee: tstee: Add initial Trusted Services TEE driver

[Balint Dobszay]

On 19 Oct 2023, at 16:16, Jens Wiklander wrote:
> On Tue, Oct 17, 2023 at 1:14 PM Sumit Garg <sumit.garg at linaro.org> wrote:
>> On Mon, 16 Oct 2023 at 13:27, Jens Wiklander <jens.wiklander at linaro.org> wrote:
>>> On Fri, Oct 13, 2023 at 1:38 PM Sumit Garg <sumit.garg at linaro.org> wrote:
>>>> On Tue, 10 Oct 2023 at 21:11, Balint Dobszay <balint.dobszay at arm.com> wrote:
>>>>> On 3 Oct 2023, at 17:42, Sumit Garg wrote:
>>>>>> On Wed, 27 Sept 2023 at 20:56, Balint Dobszay <balint.dobszay at arm.com> wrote:

[snip]

>>>>>>> +static int tstee_invoke_func(struct tee_context *ctx, struct tee_ioctl_invoke_arg *arg,
>>>>>>> +                            struct tee_param *param)
>>>>>>> +{
>>>>>>> +       struct tstee *tstee = tee_get_drvdata(ctx->teedev);
>>>>>>> +       struct ffa_device *ffa_dev = tstee->ffa_dev;
>>>>>>> +       struct ts_context_data *ctxdata = ctx->data;
>>>>>>> +       struct ffa_send_direct_data ffa_data;
>>>>>>> +       struct tee_shm *shm = NULL;
>>>>>>> +       struct ts_session *sess;
>>>>>>> +       u32 req_len, ffa_args[5] = {};
>>>>>>> +       int shm_id, rc;
>>>>>>> +       u8 iface_id;
>>>>>>> +       u64 handle;
>>>>>>> +       u16 opcode;
>>>>>>> +
>>>>>>> +       mutex_lock(&ctxdata->mutex);
>>>>>>> +       sess = find_session(ctxdata, arg->session);
>>>>>>> +
>>>>>>> +       /* Do this while holding the mutex to make sure that the session wasn't closed meanwhile */
>>>>>>> +       if (sess)
>>>>>>> +               iface_id = sess->iface_id;
>>>>>>> +
>>>>>>> +       mutex_unlock(&ctxdata->mutex);
>>>>>>> +       if (!sess)
>>>>>>> +               return -EINVAL;
>>>>>>> +
>>>>>>> +       opcode = lower_16_bits(arg->func);
>>>>>>> +       shm_id = lower_32_bits(param[0].u.value.a);
>>>>>>> +       req_len = lower_32_bits(param[0].u.value.b);
>>>>>>> +
>>>>>>> +       if (shm_id != 0) {
>>>>>>> +               shm = tee_shm_get_from_id(ctx, shm_id);
>>>>>>> +               if (IS_ERR(shm))
>>>>>>> +                       return PTR_ERR(shm);
>>>>>>> +
>>>>>>> +               if (shm->size < req_len) {
>>>>>>> +                       pr_err("request doesn't fit into shared memory buffer\n");
>>>>>>> +                       rc = -EINVAL;
>>>>>>> +                       goto out;
>>>>>>> +               }
>>>>>>> +
>>>>>>> +               handle = shm->sec_world_id;
>>>>>>> +       } else {
>>>>>>> +               handle = FFA_INVALID_MEM_HANDLE;
>>>>>>> +       }
>>>>>>> +
>>>>>>> +       ffa_args[TS_RPC_CTRL_REG] = TS_RPC_CTRL_PACK_IFACE_OPCODE(iface_id, opcode);
>>>>>>> +       ffa_args[TS_RPC_SERVICE_MEM_HANDLE_LSW] = lower_32_bits(handle);
>>>>>>> +       ffa_args[TS_RPC_SERVICE_MEM_HANDLE_MSW] = upper_32_bits(handle);
>>>>>>> +       ffa_args[TS_RPC_SERVICE_REQ_LEN] = req_len;
>>>>>>> +       ffa_args[TS_RPC_SERVICE_CLIENT_ID] = 0;
>>>>>>> +
>>>>>>> +       arg_list_to_ffa_data(ffa_args, &ffa_data);
>>>>>>> +       rc = ffa_dev->ops->msg_ops->sync_send_receive(ffa_dev, &ffa_data);
>>>>>>
>>>>>> I haven't dug deeper into the ABI yet, which is something I will look
>>>>>> into. But these RPC commands caught my attention. Are these RPC calls
>>>>>> blocking in nature? Is there a possibility that these could cause CPU
>>>>>> stalls? Do the Linux interrupts remain unhandled until the RPC calls
>>>>>> return?
>>>>>
>>>>> Yes, that is correct. We did encounter CPU stalls indeed, our solution
>>>>> was to enable preemption of S-EL0 SPs in OP-TEE [3] which solved the
>>>>> issue.
>>>>
>>>> I would have preferred to unite FFA_INTERRUPT and
>>>> OPTEE_FFA_YIELDING_CALL_RETURN_INTERRUPT since underneath both are
>>>> using FFA ABI.
>>>>
>>>> Jens,
>>>>
>>>> Can we change OP-TEE to use FFA_INTERRUPT as well when using FFA ABI?
>>>
>>> No, OP-TEE uses managed exit. Among other advantages, it allows
>>> resuming execution on a different CPU.
>>>
>>
>> I suppose that should be the case with FFA_INTERRUPT too. OP-TEE
>> should be able to resume SPs on different CPUs as well, right?
>
> Possibly, but I leave that to Balint and company to sort out if that's
> desired or not.

FF-A mandates that S-EL0 SPs have a single execution context, run only
on a single PE in the system at any point of time and are capable of
migrating. Also, FF-A allows resuming a S-EL0 SP on a different CPU
after it gets preempted by a NS interrupt. I think OP-TEE as S-EL1 SPMC
does support this, but I don't have a setup yet that would explicitly
test this scenario.

Managed exit is only available for S-EL1 SPs.

Regards,
Balint